Electroslag remelting is a secondary melting or refining process. Primary production ingots, known as consumable electrodes, are remelted and allowed to resolidify under more exactly controlled conditions than can be achieved during primary melting to improve their grain structure and to remove inclusions and inclusion-forming impurities. Remelting is achieved by resistance heating, with the electric current passing between the consumable electrode and a second electrode. The consumable electrode is partially immersed in a layer of slag, in which Joule heat for melting is generated. A pool of molten metal forms below the slag. The slag provides a path for the current. It also removes inclusions and inclusion-forming impurities from the melt.
The electric current is conventionally passed through the slag between the consumable electrode and the ingot. Such a procedure works very well in those instances where the ingot being formed has a cross section which is substantially the same size or larger than the cross section of the electrode(s) being melted. Such a procedure is undesirable in those instances where the cross section of the ingot being formed is smaller than the cross section of the electrode(s) being melted, such as in those instances where the ingot being formed is a bar. Ingots of smaller cross sections would necessitate frequent cutting. Cutting interrupts the current path, necessitating current removal by sliding contacts against the ingot. Sliding contacts are troublesome in that the ingots being formed are often neither smooth nor clean.
A current path which includes the ingot is also susceptible to another problem in those instances where the ingot being formed is smaller than the electrode being melted. The high current required to melt the consumable electrode could resistively heat the ingot and retard its solidification.
A need to establish an alternative current path existed. Experiments were conducted with the electric current being passed through the slag between the consumable electrode and the crucible. This resulted in instability in the operation of the furnace and damage to the crucible. It was hypothesized that a layer of slag froze adjacent to the crucible wall and that this layer of slag precipitated arcing thereacross. The crucible was water-cooled.